In recent years, optical communication using optical fibers has been widely used in broadband networks. Furthermore, optical transceivers are the devices that have been widely used to connect the optical fibers and various communication devices.
The optical transceivers include optical receivers that convert optical signals passing through the optical fibers to electrical signals and optical transmitters that convert electrical signals to optical signals and output the optical signals to higher level devices. Accordingly, specifications that conform to high-capacity, high-speed data transmissions are desirable and furthermore, reducing the size and manufacturing costs are also desirable.
To meet these demands, the capability and the reliability of the optical devices are enhanced by arranging firmware in the optical devices and rewriting the firmware instead of changing the optical devices themselves or adding any part thereto.
Furthermore, because malfunctioning, such as those caused by bugs, occurs in the firmware of the optical devices after they are shipped, customers are demanded to upgrade the firmware.
There are two types of control for the optical devices. One type of control, as a first control, is the control of the optical output. This needs to be performed because a temperature change or the like occurs in the optical devices and thus the optical output varies.
The other type of control, as a second control, is the control of stepwise increases of the optical output. This needs to be performed because, for example, when a higher level device or the like is started, a sudden optical output from the optical devices may cause an electric current greater than the rated current to pass, resulting in a failure of the optical devices.
To perform the first control and the second control, the optical devices usually perform feedback control with respect to the optical output. The feedback control will be described with reference to the drawings.
FIG. 20 is a schematic diagram illustrating feedback control. First, a monitor 50b obtains an optical output from a light source (for example, an LD) included in a light source 50a. 
Then, the monitor 50b monitors the operation state of the optical output and outputs, to a feedback information creating circuit 50c, monitor information indicating the monitored optical output.
Thereafter, in accordance with the monitor information that is input from the monitor 50b, the feedback information creating circuit 50c creates feedback information and outputs the created feedback information to an analog circuit 50d. Hereinafter, the information created by the feedback information creating circuit 50c in this way is referred to as “feedback information”.
The analog circuit 50d outputs the feedback information to an analog-to-digital converter (ADC) 50e. Then, the ADC 50e converts the feedback information obtained from the analog circuit 50d from analog information to digital information and outputs it to a firmware circuit 50f. 
The firmware circuit 50f includes firmware that defines various specifications of an optical device 50 and obtains the digitized feedback information from the ADC 50e. In the following, the firmware included in the firmware circuit 50f is simply referred to as “firmware”.
Then, the firmware circuit 50f creates, from the obtained feedback information, control information for controlling the output level of the light source 50a. In this way, the “control information” indicates information on the control of the optical output and indicates information created from the feedback information by the firmware in the optical device.
Examples of the control information include information, such as 1040 least significant bit (LSB). The LSB indicates the minimum digital circuit; for example, if 1 volt (V) is divided into 1000, 1 millivolt (mV) is 1 LSB.
Then, the firmware circuit 50f outputs the created control information to a digital-to-analog converter (DAC) 50g. The DAC 50g converts the control information obtained from the firmware circuit 50f to analog information and outputs the converted information to the analog circuit 50d. 
Thereafter, the analog circuit 50d outputs the information (for example, a control signal) obtained from the DAC 50g to the light source 50a and performs control of the optical output. In this way, the optical device 50 performs feedback control that controls the optical output.
In the following, the control performed by the optical device 50 when firmware is in the process of being upgraded will be described. FIG. 21 is a schematic diagram illustrating control performed by the optical device at the time of an upgrade.
The symbol “t0” illustrated in FIG. 21 indicates the start time of the rising of the optical output and the start time of the feedback control. The symbol “t1” indicates the completion time of the rising of the optical output.
The symbol “t2” indicates the start time of the upgrade of the firmware. The symbol “t3” indicates the completion time of the upgrade of the firmware that was started at “t2”.
From “t0” to “t1”, the firmware circuit 50f outputs the control information in such a manner that the optical output does not suddenly increase but gradually increase. Then, the firmware circuit 50f outputs the control information that controls the optical output indicated at “t1”.
When the upgrade of the firmware is started at “t2”, the firmware circuit 50f holds the control information as the control information (for example, 1040 LSB) that is obtained immediately before the upgrade of the firmware.
Then, the firmware circuit 50f stops outputting the control information until the firmware is upgraded and holds the control information of 1040 LSB until “t3”, the time at which the upgrade is completed.
The firmware is not upgraded from “t0” to “t2”. The operation state of the firmware at the time of not being upgraded is assumed to be in “normal operation”.
Thereafter, if the upgrade has been completed, the firmware circuit 50f resumes outputting the control information (1040 LSB) that is held before the starting of the upgrade and the optical device 50 resumes performing the feedback control.
In this way, the optical device 50 stops the feedback control when the upgrade is started and controls to simply hold the control information obtained immediately before the upgrade. Then, after the completion of the upgrade, the optical device 50 resumes the feedback control in accordance with the control information that is held.
As a technology for performing an update process on firmware that is used in an information processing system, a technology is disclosed in which, by arranging a device that stores therein the latest-version firmware and arranging a device that stores therein currently active firmware, if it is determined that, for example, the currently active firmware in the information processing system is different from the latest version firmware, the latest version firmware is downloaded in order to perform an update process on the currently active firmware (for example, Japanese Laid-open Patent Publication No. 11-003213).
However, with the technology described above, the optical device does not perform feedback control during the upgrade of the firmware. Accordingly, there is a problem in that the optical output is not properly controlled.
Such a case will be specifically described with reference to FIGS. 20 and 22. FIG. 22 is a schematic diagram illustrating the state of an optical output at the time of an upgrade.
The symbol “t10” illustrated in FIG. 22 indicates the rising of the optical output and the start time of the feedback control performed by the optical device 50. The symbol “t11” indicates the start time of the upgrade of the firmware that is performed before the rising of the optical output. The symbol “t12” indicates the completion time of the upgrade of the firmware that was started at t11.
The symbol “t13” indicates the completion time of the rising of the optical output that was started at “t10”. The symbol “t14” indicates the resumption time of the upgrade of the firmware during normal operation. The symbol “t15” indicates the completion time of the upgrade of the firmware that was started at “t14”.
First, at “t11”, the optical device 50 temporarily stops the feedback control that controls the optical output, holds the control information obtained immediately before the upgrade of the firmware was started, and resumes control of outputting the optical output at “t12”.
Accordingly, from “t11” to “t12”, the optical device 50 does not perform the feedback control on the optical output and thus the control of the optical output temporarily stops. The rising of the optical output would be completed before “t13” if the firmware is not upgraded; however, the rising and the completion of the optical output are delayed due to being affected by the upgrade.
In contrast, from “t14” to “t15”, if, for example, a temperature change occurs in the optical device 50, the optical output indicated at “t14” differs from that indicated at “t15” due to being affected by the temperature change.
From “t14” to “t15”, because the optical device 50 holds the control information obtained at “t14” and temporarily stops the feedback control, the optical device 50 does not have the control information associated with the optical output indicated at “t15”.
Accordingly, even when the upgrade is completed and the optical device 50 resumes the feedback control, the optical device 50 does not have the control information associated with the temperature change after the upgrade and thus does not control the optical output in accordance with the temperature change.